Spectators catch amazing sight of blue whales in Auckland's Hauraki Gulf

Spectators in Auckland have been stunned to see blue whales frolicking in the Hauraki Gulf.

The rare whales have been seen swimming around the Hauraki Gulf Marine Park and delighting passengers aboard the Auckland Whale & Dolphin Safari boats.

Typically the smaller Bryde's whale is seen in the area, but there was no mistaking the blue whale tail (flukes) appearing out of the water on several occasions.

It's believed the whales may be of the pygmy blue variety, slightly smaller than its Antarctic cousins.

The tour boat saw around four of the whales on July 18, including a mother and a young calf feeding from her.

More than 700 pygmy blue whales are believed to live around New Zealand, most commonly found near the South Taranaki Bight.

Sightings are rare but have increased in 2018, but Auckland Whale & Dolphin Safari said they aren't yet sure why.

"It's very exciting and intriguing as we don't know yet why there's been a sudden increase in sightings," the company said in a statement.

"Feeding behaviour has been observed in some of the whales so this is likely the reason they are staying around - where you find whales and dolphins is usually where their food is."

TV fishing show presenter Clarke Gayford took to Twitter to praise the whale and the Hauraki Gulf, saying residents were very lucky.

"Great to see the 40 resident Bryde's Whales happy to share their space with some Blues," he said.

"Which coast did the Welly whale head up? Some sort of conference? Have said it before but we don't know how lucky we are with the Hauraki Gulf on our doorstep."

Newshub.